Journal of virology
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Journal of virology · Jun 2014
A conformation-dependent neutralizing monoclonal antibody specifically targeting receptor-binding domain in Middle East respiratory syndrome coronavirus spike protein.
Prophylactic and therapeutic strategies are urgently needed to combat infections caused by the newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV). Here, we have developed a neutralizing monoclonal antibody (MAb), designated Mersmab1, which potently blocks MERS-CoV entry into human cells. Biochemical assays reveal that Mersmab1 specifically binds to the receptor-binding domain (RBD) of the MERS-CoV spike protein and thereby competitively blocks the binding of the RBD to its cellular receptor, dipeptidyl peptidase 4 (DPP4). Furthermore, alanine scanning of the RBD has identified several residues at the DPP4-binding surface that serve as neutralizing epitopes for Mersmab1. These results suggest that if humanized, Mersmab1 could potentially function as a therapeutic antibody for treating and preventing MERS-CoV infections. Additionally, Mersmab1 may facilitate studies of the conformation and antigenicity of MERS-CoV RBD and thus will guide rational design of MERS-CoV subunit vaccines. ⋯ MERS-CoV is spreading in the human population and causing severe respiratory diseases with over 40% fatality. No vaccine is currently available to prevent MERS-CoV infections. Here, we have produced a neutralizing monoclonal antibody with the capacity to effectively block MERS-CoV entry into permissive human cells. If humanized, this antibody may be used as a prophylactic and therapeutic agent against MERS-CoV infections. Specifically, when given to a person (e.g., a patient's family member or a health care worker) either before or after exposure to MERS-CoV, the humanized antibody may prevent or inhibit MERS-CoV infection, thereby stopping the spread of MERS-CoV in humans. This antibody can also serve as a useful tool to guide the design of effective MERS-CoV vaccines.
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Journal of virology · Jun 2014
Augmented replicative capacity of the boosting antigen improves the protective efficacy of heterologous prime-boost vaccine regimens.
Prime-boost immunization regimens have proven efficacious at generating robust immune responses. However, whether the level of replication of the boosting antigen impacts the magnitude and protective efficacy of vaccine-elicited immune responses remains unclear. To evaluate this, we primed mice with replication-defective adenovirus vectors expressing the lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP), followed by boosting with either LCMV Armstrong, which is rapidly controlled, or LCMV CL-13, which leads to a more prolonged exposure to the boosting antigen. Although priming of naive mice with LCMV CL-13 normally results in T cell exhaustion and establishment of chronic infection, boosting with CL-13 resulted in potent recall CD8 T cell responses that were greater than those following boosting with LCMV Armstrong. Furthermore, following the CL-13 boost, a greater number of anamnestic CD8 T cells localized to the lymph nodes, exhibited granzyme B expression, and conferred improved protection against Listeria and vaccinia virus challenges compared with the Armstrong boost. Overall, our findings suggest that the replicative capacity of the boosting antigen influences the protective efficacy afforded by prime-boost vaccine regimens. These findings are relevant for optimizing vaccine candidates and suggest a benefit of robustly replicating vaccine vectors. ⋯ The development of optimal prime-boost vaccine regimens is a high priority for the vaccine development field. In this study, we compared two boosting antigens with different replicative capacities. Boosting with a more highly replicative vector resulted in augmented immune responses and improved protective efficacy.
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Journal of virology · Jun 2014
Comparative StudyHigh level of vector competence of Aedes aegypti and Aedes albopictus from ten American countries as a crucial factor in the spread of Chikungunya virus.
Chikungunya virus (CHIKV) causes a major public health problem. In 2004, CHIKV began an unprecedented global expansion and has been responsible for epidemics in Africa, Asia, islands in the Indian Ocean region, and surprisingly, in temperate regions, such as Europe. Intriguingly, no local transmission of chikungunya virus (CHIKV) had been reported in the Americas until recently, despite the presence of vectors and annually reported imported cases. Here, we assessed the vector competence of 35 American Aedes aegypti and Aedes albopictus mosquito populations for three CHIKV genotypes. We also compared the number of viral particles of different CHIKV strains in mosquito saliva at two different times postinfection. Primarily, viral dissemination rates were high for all mosquito populations irrespective of the tested CHIKV isolate. In contrast, differences in transmission efficiency (TE) were underlined in populations of both species through the Americas, suggesting the role of salivary glands in selecting CHIKV for highly efficient transmission. Nonetheless, both mosquito species were capable of transmitting all three CHIKV genotypes, and TE reached alarming rates as high as 83.3% and 96.7% in A. aegypti and A. albopictus populations, respectively. A. albopictus better transmitted the epidemic mutant strain CHIKV_0621 of the East-Central-South African (ECSA) genotype than did A. aegypti, whereas the latter species was more capable of transmitting the original ECSA CHIKV_115 strain and also the Asian genotype CHIKV_NC. Therefore, a high risk of establishment and spread of CHIKV throughout the tropical, subtropical, and even temperate regions of the Americas is more real than ever. ⋯ Until recently, the Americas had never reported chikungunya (CHIK) autochthonous transmission despite its global expansion beginning in 2004. Large regions of the continent are highly infested with Aedes aegypti and Aedes albopictus mosquitoes, and millions of dengue (DEN) cases are annually recorded. Indeed, DEN virus and CHIK virus (CHIKV) share the same vectors. Due to a recent CHIK outbreak affecting Caribbean islands, the need for a Pan-American evaluation of vector competence was compelling as a key parameter in assessing the epidemic risk. We demonstrated for the first time that A. aegypti and A. albopictus populations throughout the continent are highly competent to transmit CHIK irrespective of the viral genotypes tested. The risk of CHIK spreading throughout the tropical, subtropical, and even temperate regions of the Americas is more than ever a reality. In light of our results, local authorities should immediately pursue and reinforce epidemiological and entomological surveillance to avoid a severe epidemic.
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Journal of virology · May 2014
Development of an adenovirus-based respiratory syncytial virus vaccine: preclinical evaluation of efficacy, immunogenicity, and enhanced disease in a cotton rat model.
The lack of a vaccine against respiratory syncytial virus (RSV) is a challenging and serious gap in preventive medicine. Herein, we characterize the immunogenicity of an adenovirus serotype 5-based RSV vaccine encoding the fusion (F) protein (Ad5.RSV-F) and the protection provided following immunization with Ad5.RSV-F and assess its potential for producing enhanced disease in a cotton rat (CR) model. Animals were immunized intranasally (i.n.) and/or intramuscularly (i.m.) and subsequently challenged with RSV/A/Tracy (i.n.) to assess protection. Robust immune responses were seen in CRs vaccinated with Ad5.RSV-F given i.m. or i.n., and these responses correlated with reduced replication of the virus in noses and lungs after challenge. Neutralizing antibody responses following immunization with a single dose of Ad5.RSV-F at 1 × 10(11) viral particles (v.p.) elicited antibody titers 64- to 256-fold greater than those seen after natural infection. CRs boosted with Ad5.RSV-F i.n. 28 days after an i.m. dose also had significant increases in neutralizing antibody titers. Antibody affinity for different F-protein antigenic sites revealed substantial differences between antibodies elicited by Ad5.RSV-F and those seen after RSV infection; differences in antibody profiles were also seen between CRs given Ad5.RSV-F i.m. and CRs given Ad5.RSV-F i.n. Ad5.RSV-F priming did not result in enhanced disease following live-virus challenge, in contrast to the histopathology seen in CRs given the formalin-inactivated RSV/A/Burnett vaccine. ⋯ Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in infants and young children and a serious health threat in the immunocompromised and the elderly. Infection severity increased in children in an immunization trial, hampering the over 4-decade-long quest for a successful RSV vaccine. In this study, we show that a genetically engineered RSV-F-encoding adenoviral vector provides protective immunity against RSV challenge without enhanced lung disease in cotton rats (CRs). CRs were vaccinated under a number of different regimens, and the immunity induced by the recombinant adenoviral RSV vaccine administered by use of an intramuscular prime-intranasal boost regimen may provide the best protection for young infants and children at risk of RSV infection, since this population is naive to adenoviral preformed immunity. Overall, this report describes a potential RSV vaccine candidate that merits further evaluation in a phase I clinical study in humans.
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Influenza viruses of the H6 subtype have been isolated from wild and domestic aquatic and terrestrial avian species throughout the world since their first detection in a turkey in Massachusetts in 1965. Since 1997, H6 viruses with different neuraminidase (NA) subtypes have been detected frequently in the live poultry markets of southern China. Although sequence information has been gathered over the last few years, the H6 viruses have not been fully biologically characterized. To investigate the potential risk posed by H6 viruses to humans, here we assessed the receptor-binding preference, replication, and transmissibility in mammals of a series of H6 viruses isolated from live poultry markets in southern China from 2008 to 2011. Among the 257 H6 strains tested, 87 viruses recognized the human type receptor. Genome sequence analysis of 38 representative H6 viruses revealed 30 different genotypes, indicating that these viruses are actively circulating and reassorting in nature. Thirty-seven of 38 viruses tested in mice replicated efficiently in the lungs and some caused mild disease; none, however, were lethal. We also tested the direct contact transmission of 10 H6 viruses in guinea pigs and found that 5 viruses did not transmit to the contact animals, 3 viruses transmitted to one of the three contact animals, and 2 viruses transmitted to all three contact animals. Our study demonstrates that the H6 avian influenza viruses pose a clear threat to human health and emphasizes the need for continued surveillance and evaluation of the H6 influenza viruses circulating in nature. ⋯ Avian influenza viruses continue to present a challenge to human health. Research and pandemic preparedness have largely focused on the H5 and H7 subtype influenza viruses in recent years. Influenza viruses of the H6 subtype have been isolated from wild and domestic aquatic and terrestrial avian species throughout the world since their first detection in the United States in 1965. Since 1997, H6 viruses have been detected frequently in the live poultry markets of southern China; however, the biological characterization of these viruses is very limited. Here, we assessed the receptor-binding preference, replication, and transmissibility in mammals of a series of H6 viruses isolated from live poultry markets in southern China and found that 34% of the viruses are able to bind human type receptors and that some of them are able to transmit efficiently to contact animals. Our study demonstrates that the H6 viruses pose a clear threat to human health.